Concern Regarding "A Non-Inflationary Solution to the Entropy Problem of Standard Cosmology."

TL;DR

This paper examines whether non-inflationary solutions can address key cosmological problems at high energy scales, analyzing a multidimensional scenario and highlighting the importance of residual bulk energy during extra-dimensional contraction.

Contribution

It introduces a new scaling solution during extra-dimensional contraction and assesses the viability of non-inflationary solutions at very high energy scales.

Findings

Residual bulk energy density influences the evolution during extra-dimensional contraction

A new scaling solution during contraction of extra dimensions is identified

The validity of effective field theory at 10^{25} GeV is questionable

Abstract

We discuss the entropy and the size/homogeneity/horizon problems in power-law expanding universes with one scale initial conditions. We set the minimal scale $\Lambda = 10^{25}$ GeV at which a non-inflationary solution is possible and show that the radiation dominated epoch alone technically is not able to explain the issue. An earlier paper on the subject, [1], attempts a multidimensional scenario. We review the scenario of the paper [1] in an effective four dimensional Einstein frame. We find that during contraction of extra dimensions, the residual bulk energy density is important and leads to a scaling solution. The existence of this scaling solution is a new result. We provide a numerical example which demonstrates the evolution of the scale factor and the extra dimensions. In the whole, the validity of the effective field theory calculations at the scale of $\Lambda = 10^{25}$ GeV is under question and, hence, the final conclusion regarding the possibility of a non-inflationary solution is preliminary.